Control of direct-current machines.



C. W. GIRVIN.

CONTROL OF DIRECT CURRENT MACHINES.

APPLICATION FILED JUNE 12. 1913.

1,1 96,7 74. Patented Sept. 5, 1916.

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WITNESSES [NYE/(T01? A TTOHNE U. W. GIRVIN.

CONTROL OF DIRECT CURRENT MACHINES.

APPLlCATlON FILED JUNE 12, 1913.

Patented Sept. 5, 1916.

9 SHEETS-SHEET 2.

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CONTROL OF DIRECT CURRENT MACHINES.

APPLICATION FILED JUNE 12. 1913.

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C. W. GIRVIN.

CONTROL OF DIRECT CURRENT MACHINES.

APPLICATION FILED JUNE I2. 1913.

1 1 96- 4. Patented Sept. 5, 1916.

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CONTROL OF DIRECT CURRENT MACHINES.

APPLICATION FILED JUNE 12. I913.

1,1 96,774. PatentedSept. 5, 1916.

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CONTROL OF DIRECT CURRENT MACHINES.

APPLlCATION FILED JUNE 12, 1913.

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APPLICATION FILED JUNE 12. 1913.

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Patented Sept. 5, 1916.

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C. W. GIRVIN.

CONTROL OF DIRECT CURRENT MACHINES.

APPLICATION FILED JUNE 12. 1913.

1 1 96,7 74. Patented Sept. 5, 1916.

9 SHEETSSHEET 8.

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CONTROL OF DIRECT CURRENT MACHINES.

APPLICATION FILED JUNE 12, I913- Patented Sept. 5, 1916.

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avwemtoz when used in connection with UNITED STATES PATENT CHARLES W.GIRVIN, OF SAN FRANCISCO TRICAL HAWAII, A CORPORATION OF OFFICE.

CALIFORNIA, ASSIGNOR TO GIRVIN ELEC- DEVELOPMENT COMPANY, LIMITED, OF

HONOLULU, TERRITORY OF THE TERRITORY OF HAWAII.

CONTROL OF DIRECT-CURRENT MACHINES.

Specification of Letters Patent.

Patented Sept. 5, 1916.

Application filed June 12, 1913. Serial No. 773,204.

To all whom it may concern Be it known that I, CHARLEs W. GmvIN, acitizen of the United States, and residing at San Francisco, in thecounty of San Francisco and State of California, have invented certainnew and useful Improvements in Control of Direct-Current Machines, ofwhich the following is a specification.

This invention relates to the control of direct current machines, as forinstance, the voltage control when employed in connec tion withgenerators and the speed" control motors, by varying the number ofarmature conductors in series. Heretofore, attempts have been made alongsomewhat similar lines to control direct current machines as aboveindicated, but these attempts, so far as I am aware of, have notproduced satisfactory results for various reasons.

One reason lies in the fact that direct cur rent machines as heretoforeprovided have their armature windings in a closed circuit with at leasttwo paths in parallel from positive to negative brushes. Thisnecessitates an equal number of armature turns in series in eachparallel path; consequently the varying of the number of turns in seriesmust be exactly concurrent in the several parallel paths in order topreventserious unbalancing of the E. M. F.s in said paths, suchunbalancing having the effect of causing large local currents in thearmature and serious sparking at the brushes.

Another reason lies in the fact that commercial direct current machinesgenerally employ a rotating armature making it a difficult matter tosuccessfully cut in or cut out armature turns while the machine is inoperation, excepting by the use of intricate and expensive apparatus forthis purpose. lVhile attempts have been made to vary this by providing astationary armature in which the usual methods of providing parallelpaths are employed, the necessary change in brush mounting, etc., actsto prevent successful control in this manner. These general difficultiesprevent the practical employment of this method of control, but areEnglish Patent N 0. 22,270 of 1912, the disclosure of which correspondsin general to that of my application for Letters Patent filed March 11,1912, Serial No. 683,065, in which a stationary armature is employed,the armature having its windings connected constantly in series and incircuit, thus proylding a single series path through the Winding. Thisenables turns or windings to be cut out of circuit as desired withoutany unbalancing effect, the remaining windings or turns continuing inseries and in circuit. As the armature is stationary, the windings orturns are readily accessible, permitting variations in the number ofturns in series to be readily made during the operation of the machine.A machine embodying the gen eral ideas of said prior application isshown diagrammatically in the drawings and more speci cally referred tohereinafter,the drawings showing one group of coil units having theseries relationship, but as in said prior disclosure, the arrangement ofcoil units may provide for a plurality of groups, as for instance, two,four, eight, etc., according to the use to which the machine is to beput, provisions being made for connecting groups in series, in parallel,or a combination of both, this arrangement enabling these desirablechanges to be employed in the control and at the same time eliminatingthe disadvantages heretofore referred to, and without th requirement ofan impracticable number of commutators.

The objects of my invention are therefore to provide a method ofcontrolling direct current machines which .will permit of the variationin number of turns or windings in series; which will permit of theemployment of the series, parallel-series, or parallel variations; andwhich will eliminate the difficulties heretofore encountered inattempting to employ this type of control in direct current machines.Also to provide simple and efficient apparatus for the carrying of themethod into effect.

To these and other ends, the nature of which will be readily understoodas the invention is hereinafter disclosed, my invention consists in theimproved construction and combination and arrangement of elementshereinafter fully described, illustrated in the accompanying drawingsand more particularly pointed out in the appended claims.

In the accompanying drawings in which similar reference charactersindicate similar parts in each of the views :-Figure 1 is a diagrammaticdevelopment of a direct current machine illustrating the generalprinciples of my, invention when employed in connection with a singlegroup. Fig. 2 is a diagrammatic development in plan view of sufiicientportions of Fig. 1 to illustrate the general operation. Figs. 3 to 7inclusive are fragmentary diagrammatic views of a commutator arrangementshowing the method of commutation of coil units or windings of thearmature preferably employed in a machine in which the control is of thetype disclosed in the drawings. Figs. 8, 9 and 10 are detaileddiagrammatic views illustrating one way in which a coil or winding maybe cut out of circuit. Fig. 11 is a diagrammatic view of a diiferenttype of arrangement for performing this service. Fig. 12 is adiagrammatic representation of a machine having four groups, the viewshowing the general arrangement of coil units with the terminals of thegroups indicated, this arrangement permitting of the change in the formof group connections, the specific changes being shown in Figs. 13 and14:. Fig. 13 is a composite view showing the four groups of Fig. 12in-series relationship, the successive views illustratingdiagrammatically one order in which coil' units may be cut out for thepurpose of controlling the voltage or sp'eed of the machine shown inFig. 12. Fig. 14 is a similar view showing the sequence where the groupsare changed from series to parallel relation through an intermediateparallel-series relation, the view also showing intermediate stepsprovided by cutting out coil units as in Fig. 13,'the diagrammaticillustrations of Figs. 13 and 14 indicating what may be termed runningpoints in the control. Fig. 15 is a similar View showing a possibleintermediate sequence to provide running points between the positions ofFig. 13 and those of Fig. 14. Fig.

'16 is a diagrammatic view illustrating one way in which the variouscircuits of a four group arrangement with a master controller may beprovided to eifect the various combinations shown in Figs. 13, 14 and15. Fig. 17 is a diagrammatic view of the field and commutating p'olewinding employed in connection with Fig. 16. Fig. 18 is a view similarto Fig. 16, showing, however, a different field winding arrangement.Fig. 19 is a view similar to Fig. 17 with the field winding arranged asin Fig. 18. Fig. 20 is a table or diagram indicating the positions ofthe several switches in the different control steps or notches toproduce the running points indicated in Figs. 13, 14 and 15.

As heretofore pointed out, the present invention is more particularlyadapted for use in connection with direct current machines of the typedisclosed in the patent and 'application heretofore identified, in whicha stationary armature and a rotating field are employed to providealternating E. M. F.s with E. M. F. time-values of definite phaserelationship, the arrangement of the commutator being such that the coilunits or windings of the armature are acted upon individually, apredetermined number being maintained in constant series relationshipand constantly in circuit, this series relationship providing a singlepath from terminal to terminal of this predetermined number; thispredetermined number may be termed a group, and the machine may have asingle group or a plurality of groups, these groups being adapted to beplaced in series or other relationships without afiectingthe series andcircuit relationships referred to. The manner of arranging thecommutator segments and connections to provide this result isillustrated diagrammatically in Figs. 3 to 7 which show diagrammaticsectional views of a commutator operating in connection with four coilunits or windings as a group, the view showing the changes in theconnections ot the several windings when their E. M. F.s have beensuccessively reversed, the coil units being indicated at a, b, c and d,the terminals at T and T, the segments at S, the connections at C, thearrows indicating the direction of current flow. As will be seen fromthese views, each coil unit has its terminals in the form of brushes,the latter being adapted to ride on the surfaces of the commutatorsegments, the connections between the several coil units being providedby the connections C of the commutator segments. As the direction of E.M. F. of a coil unit reverses in the operation of the machine, themanner in which its terminals (brushes) are connected with adjacentunits also changes, as shown for instance in the change of connectionsof coil unit a shown in Figs. 3 and 4, so that the single series paththrough the series of coil units is maintained throughout the variouschanges produced in machine operation, Figs. 3 and 7 showing reversalsof the coil units shown without affecting the continuous direction ofcurrent flow.

The number of coil units which may form a group will be determined bythe machine construction, dependent upon its use, as it is obvious thatthe entire number of coil units may form a single group by simplycontinuing connections in the manner shown. to meet the commutatingconditions, but

in each instance, the coil unit is normally an open-circuit coil unitwhich has its terminals coacting with a commutator so as to maintain itconstantly in series relation with its neighboring units and in aconstantly closed circuit. a

he control feature herein disclosed retains the above features and atthe same time provides for cutting out coil units of a group for thepurpose of varying the voltage or the speed as the case may be. This isprovided for b increasing the number of coil units or wlndi'ngs withinthe group and providing means which will enable the additional units orwindings to be cut out at will, without affecting the remaining windingsor units of the group. For example, the preferred minimum number ofwindings or units which would constitute the permanent units of thegroup is nine, this number providing a substantially continuous E. M. F.at the terminals of the group. If it is desired to provide a controlvariation by cutting out three units, three additional units or windingswould be added, thus increasing the number in the group to twelve units.If greater variations are desired, the number of coil units within thegroup may be still further increased thus increasing the number capableof being cut out without materially affecting the continuity of E. M. F.his control variation may be provided where all of the units or windingsof the machine are in a single group and therefore constantly in seriesthroughout the armature, such an arrangement being shown in Figs. 1 and2, this particular arrangement preferably employing coil units orwindings each formed of a number of conductors or coils connected inseries within the armature, the terminals of the connected coils orconductors forming the terminals of the coil unit, the coil unitterminals being two in number and each 00- operating with a commutatorby the employment of one or more brushes. In this particular type thecontrol is provided by cutting out any or all of the conductors or coilsof one or more coil units.

Vhere the control operates in connection with a plurality of groupsadditional changes can be provided by connecting the groups in series orparallel, etc., two groups permitting the change from series to paralel,four groups permitting an intermediate parallel-series condition, etc. Adiagrammatic illustration of the arrangement where four groups areemployed is shown in Fig. 12, in which the two commutators shown may becommutators of a single machine or each may be of a separate machine.

Referring more particularly to Figs. 1 and 2, a, b, c, d, etc., a, b 0 detc., a, 5 0 (1, etc., and a, b, c, d, etc., indicate coils orconductors of an armature of the type of machine referred to, thesecoils or conductors being connected to form what may be termed coilunits or windings, the terminals of each unit being in the form ofbrushes corresponding to the brushes shown in Figs. 3 to 7, thesebrushes being adapted to cooperate with the commutator 90. For

instance, the conductors indicated ata, a, a and a form one coil unit,b, b, b and 6 form another coil unit; in other words, the conductorshaving similar reference letters may be considered as forming a coilunit. As will be seen the coil units a, e, and i have their conductorsprovided with terminals cooperating with switches, while the remainingcoil units are of the general type indicated in Fig. 3, the latter coilunits forming what I have referred to as the permanent units of thegroup, the three units a, e and i being added for control purposes. Asthe arrangement shown in these fi ures provides for the cutting out ofindividual coils or conductors, the conductors are shown as being inseries relationship.

In Fig. 2 the switches are indicated at 50, 51, 52, etc., to 61, andwhen in the position shown in full lines, the conductor controlled bythe switch is in circuit, the dotted line position of the switchindicating that the conductor is cut out of circuit. stance, assumingthat all of the switches are in the full line position all of theconductors are in circuit. If switch 50 is now moved to the dotted lineposition, the conductor a will be cut out of circuit, leaving thecircuit of coil it provided by the conductors a a and a. If the switches53, 56 and 59 be successively moved to the dotted line position, theconductors (E, (t and a will be successively cut out of circuit, thuscutting out coil unit a. Similarly the successive movement of theswitches 51, 54, 57 and 60 will have the efiFect of cutting out coilunit 6 through successively cutting out its conductors. Obviously asimilar action may be had with respect to coil unit As will be seen, theconductors which are cut out are at dif ferent points, preferablyequi-spaced, thus reducing the tendency to unbalance armature reaction.

Any suitable means may be employed for providing the cutting in and outof circuit of a coil unit or conductor, one form being shown in Figs. 8,9 and 10, this arrangement permitting the conductor or unit to be cutout or cut in without opening the circuit. In these figures, assumingthe conductor a to be that shown, and 71 indicate the leads to and fromthe conductor, and 72 the lead from the coil unit circuit. The leads 70and 71 are shown as connected to terminals on a fixed block 73, whilethe lead 72 is shown as connected to terminals carried For in-- movableblock 74, said lead being provided with a resistance 72 'between theterminals.

In Fig. 10 the conductor a is shown as in circuit, the position of theblock 74. being such as to provide this efi'ect. Fig. 8 shows the block74 as having been moved to a position where the conductor a is cut outof the circuit. In passing from one of these positions to the other, theblock is moved through an intermediate position shown in Fig. 9, theconductor a being shunted by the resistance "('2 while in the positionof Fig. 9, thus providing for the cutting in or out operation withoutopening the circuit, this being a well known method which may beemployed for this purpose.

As will be readily understood, the cutting out of a conductor will havethe effect of reducing the terminal voltage if employed in connectionwith a generator, or of increasing the speed where employed inconnection with a motor. And since the conductors are carried by astationary armature, it will be readily understood that this cuttmg inand out operation may be performed without difficulty while the machineis in'operation.

While I have shown in Figs. 1 and 2 the idea as applied to the cuttingout of individual conductors of a coil unit, a preferred arrangement isto cut out coil units as an entirety such an arrangement being shown inFig. 12 in which the units are shown as forming four groups, the unitsof each group being connected in series through the commutatorarrangement, said view illustrating a general switching operationsimilar to that shown in Fig. 2, excepting that each switch controls acoil unit as an entirety.

By providing for cutting out coil units by a as in Fig. 12, it ispossible to employ any desired arrangement in the conductors forming thecoil unit, enabling the conductors to be arranged in series, parallel ora combination of both as may cutting out of individual conductors isemployed as in Fig. 2, the arrangement practically requires that theconductors be in series.

The general idea shown in Fig. 12 enables the invention to beparticularly adapted for use in controlling the speed of motors,especially where the latter are used for railway work, or otheroperations Where wide variations in motor speed are desirable. Examplesof these are shown in Figs. 13 to 20, which represent a plurality ofcoil units arranged in four groups; the coil units may be in one motoror in two motors as desired, the operation being substantially the samein either case, the use of two motors providing a possible advantage inenabling the be desired. Where the.

changes to be made without entirely opening the circuit as presentlyexplained.

In Fig. 13 I have shown diagrammatically a series of running positionswhich may be provided by the cutting out operation heretofore referredto with respect to Fig. 12, these diagrammatic views being successivelyarranged, with each group having twelve coil units, the arrangementproviding for the cutting out of three coil units from each group. Thesethirteen views disclose running positions where the groups are inseries. For instance, in the first position all of the twelve coil unitsof each group are in circuit; in the second position one coil unit ofthe first group is cut out of circuit; in

the third position a second coil unit of that group is cut out, while inthe fourth position the third unit of that group is cut out, theremaining groups having all their coil units in circuit. The nextposition retains the first group with nine units in circuit and cuts outone unit of the second group. As will be seen, this successive cuttingout of units is continued until position XIII is reached, this positionindicating that only the permanent coil units of each group remain incircuit.

Fig. 14 shows seven positions XIV to XX in which the groups are inparallel-series relation, the cutting out of coil units insequence beingindicated. In these seven positions it is seen that two coil units arecut out at each step, this being necessitated by the parallel connectionof two groups. Said figure also shows, in positions XXI to XXIV, thegroups arranged in parallel with coil units out out to effect thevarious changes desired. In these four positions it is necessary to cutout four coil units, one in each group at each step, due to the parallelrelation of groups. In these views the number of coil units in circuitis indicated by the numerals placed on the rectangles each of which isintended to represent-a group. From these positional views it will beseen that the cutting out of coil units enables variations in speed tobe provided whether the groups be connected in series, parallel-seriesor parallel, each position providing a running point and enabling thespeed to be varied within comparatively wide limits.

If desired, additional running positions may be provided as indicated inFig. 15, the positions shown therein being between positions XIII andXIV shown in Figs. 13 and 14, position XIII being equivalent to positionXIII, since the number of coil units in series is the same in bothpositions, the first group, however, being entirely out out in thepositions of Fig. 15. As will be understood, the groups of Fig. 15 arein series and form, when employed, a continuation of the positions shownin Fig. 13. The positions of Fig. 15, while possible, are such as tendto provide difliculties unless the arrangement of coil units is such asto avoid unbalancing and auxiliary devices be employed for raising thebrushes of the group out out of circuit from the commutator; hence theywould be employed only where necessary to give a more gradual increasein speed than provided for in changing from position XIII to XIV.

In Figs. 16 and 18 I have shown diagrammatically a switching arrangementand master controller for providing positions shown in Figs. 13, 14 and15, it being assumed that the motor is employed in rail way work,receiving current from a trolley and being connected to ground. Thesefigures differ from each other in that Fig. 16 shows the entire fieldwinding F W as in series with but one group, last group, thus placing itbetween the armature and the ground connection, which reduces insulationdifliculties in the field; in Fig. 18 the field is shown as divided intoas many windings, fw fw fw and f wfl as there are groups, each separatewinding being permanently in series with a separate group.

Where but a single motor is employed, the motor having the four groupsof coil units shown in Fig. 16, the field winding arrangement of thatfigure is preferred since it involves the use of but two slip rings, asindicated more particularly in Fig. 17. WVhere the four groups arearranged in two motors (for instance, the two upper groups in one motor,the two lower groups in the other motor), a field winding F W would beconnected up in each motor being in series with one of the groups ofthat motor. For instance, if the division of groups is as indicatedabove, the additional winding would be connected in series with thegroup next to the top group.

e arrangement shown in Fig. 18 employs a distinct field winding, fw fwfw and fac for each group as indicated in Fig. 19, requiring the use ofa large number of slip rings.

The object in connecting the entire field winding FW in series with butone group as in Fig. 16 is to maintain the fixed relation between thestrength of commutating pole (and compensating winding when used) andthe current in the armature conductors. It will be readily seen thatwere the field winding FW to receive all the current of four groups inparallel, as in Fig. 14, views XXI to XXIV it would be four times asstrong (neglecting saturation) as it would be when the four groups werein series as in Fig. 13, yet the current to be commutated in any oneconductor would be the same, hence difiiculties would arise.

preferably the The same object is accomplished by subdividing the fieldwindings into as many equal portions as there are groups and placingeach portion permanent y m series with a separate group as shown n Figs.18 and 19. If desired, these separate field-windings fw f'w fur, and fwcould be independent of the armature groups and placed in the variouscircuit relationships by a separate set of switches. It is obvlous thatthe necessity of maintaining the fixed relationship between armatureconductor current and field winding applies only to the auxiliaryfields, the main field winding being shown similarly connected forconvenience only.

In both Figs. 16 and 18 the general connections including switches andthe master controller are similar, so that an explana tion of Fig. 16will suffice. The coil units as a group are indicated at CU, as in Figs.13, 14 and 15, the commutator being omitted 1n F gs. 16 and 18, it beingassumed that the terminal brushes of the coil units are connected up asshown in Figs. 3 to 7, and Fig. 12. For the purposes of illustration itis assumed that current is being supplied from the trolley line T1, theground connection being indicated at G. The switches are indicated at100, 101, etc., to 124, the switch 100 being the main switch controllingthe supply, switch 101 controlling the starting resistance SR, switches102 to 112 inclusive, controlling the arrangement of groups, whileswitches 113 to 124 control the cutting in and out of individual coilunits.

Any desirable type of switches may be employed, Fig. 11 illustrating oneform of solenoid switch. Suitable methods of operating the switches maybe employed, that shown in the drawings being of low voltage supplied bya battery, Bat, this being simply an example of one of different ways inwhich such control of switch operation can be had.

MG represents the master controller in which the contacts are arrangedto provide the various positions shown in Figs. 13, 14 and 15 togetherwith the necessary transition positions, the positions shown corresponding to those indicated on the diagram of Fig. 20, the latterindicating the positions of the several switches in the differentcontrol steps or notches.

As will be seen by referring to Fig. 20, the first position places thegroups in series at the time of closing the circuit through switch 100,this position having the starting resistance SR in circuit; this is buta transition position, the first running position be ing with thestarting resistance cut out, this being shown as the second position ofthe figure, the switch 101 being closed, this being the first positionof Fig. 13. Positions 3 to 14 indicate the closing of the coil unit coilunits being cut out of opening the switch tion of Fig. 14, said latter'dicated at 31 in Fig. 20, positions 29 switches 113 to 124 forproviding the remaining running steps shown in Fig. 13, 'the groupsbeing in series.

As Figs. 16 and 20 are assumed to employ a single motor with four groupsthe change in relationships of groups is provided vby 100, this beingindicated in position 15 of Fig. 20. Positions 16 to 27 inclusive ofsaid Fig. 20 provide for the setting of switches to provide therunningpositions shown in Fig. 15, one group of circuit; as heretoforestated, this set of positions is optional. If these positions are notemployed, the succession of positions in Fig. 20 would pass from 15 to29, position 28 being that of opening the circuit when change is madefrom the final position of Fig. 13 to the first posiposition being inand30 being transition positions leading to the placing of the groups inparallel-series.

Positions 31 to 37 provlde the positions XIV to XX of Fig. 14, afterwhich the circuit is opened and the switch is reset to provide theposition 40 which corresponds .to the position XXI of Fig. 1 1, thesucceeding running positions being provided by the remaining positions11 to 43 of Fig. 20.

Where more than one motor is employed to provide the groups, thenecessity for opening the circuit for transition purposes is reduced oreliminated, the usual practice of short-circuitin'g motors beingpossible.

Inasmuch as switches 111 and 112 operate only in unison they are shownas controlled by a single circuit.

107, 108, 109 and 110 are operated by a single circuit for the samereason. This reduces the number of control circuits.

From the above it will be seen that not only is it possible to secure inone machine the control heretofore provided by the use of a plurality ofdirect current machines, in which the circuit relationships between themachine is varied, but in addition large numbers of variations in eachcircuit relationship may be had. Or, as indicated above, thesevariations are had where the groups form parts of more than one machine.As will be understood, these variations are not simply for transitionpurposes but are actual running points in the control, thus providingfor facile operation of the machine.

While I have herein shown and described several ways in which myinvention may be carried into effect, it will be readily understood thatchanges and modifications therein may be required or desired to meetindividual preferences or the exigencies of use, and I desire to beunderstood as reserving the right to make such changes or modificationsin so far as the same may fall within the 2. In direct current machines,

Similarly switches 106,

spirit and scope of the invention as exressed in the accompanyingvclaims.

' Having thus described my invention, what I claim as new is 2-- 1. Indirect current machines, a predetermined number of sources ofalternating E. M. F.s forming a polyphase group cooperating witha-commutator to provide a series circuit through the group, and meansfor varying the number of sources active in the group at will.

a predetermined number of sources of alternating E. M. F.s forming apolyphase group cooperating with a commutator to provide a seriescircuit through the group, and means for varying the number of sourcesactive in the group at will by cutting out of circuit one or more of thesources without opening the circuit. v

3. In direct current machines, a predetermined number of sources ofalternating E. M. F.s forming a group with each source permanently andindividually maintained in series and in circuit through a commutator,and one or more additional sources included within the group and adaptedto be active therein at will.

4. In direct current machines, a predetermined number of sources ofalternating E. M. F.s forming a group with each source permanently andindividually maintained in series and in'circuit through a commutator,and a plurality of additional sources included within the group andadapted to be active therein at will, said' additional sources beinginterspaced with respect to the permanent sources.

5. In direct. current machines, a predetermined number of sources ofalternating E. M. F.s, forming a plurality of groups, each group having.its sources individually cooperating with a commutator to provide aseries circuit within and through the group, and means for varying thenumber of sources active in a group at will.

6. In direct current machines, a predetermined number of sources ofalternating E. M. F.s, forming a plurality of groups, each group havingits sources individually cooperating with a commutator to provide aseries circuit within and through the group, and means for varying thenumber of sources active in each group at will.

7. In direct current machines, a predetermined number of sources ofalternating E. M. F.s, forming a plurality of groups, each groupcooperating with a commutator to provide a single circuit within andthrough the group, means for varying the number of sources active ineach group at will, and means for connecting the groups in series,parallel or a combination of both.

8. In direct current machines, a predetermined number of sources ofalternating E. In testimony whereof I ai'fix my signature M. F.s.forming a plurality ofgroups, each in presence of two witnesses.

ou coo eratln with a, commutator to govizle a s ingle cicuit within andthrough CHARLES GIRVIN' 5 the group, and'means for connecting theWitnesses:

groups in series, parallel or 21V combination of Homer: G. Snrrz, both.Enwm S. Cmnxson.

